How can I include pictures in the Newsletter created with Civicrm ?
Using the "Image" Button in Civicrm's HTML editor, the pictures appear in the newsletter template as well as in the "preview as HTML" window, but in both test e-mail and the actual e-mail they only appear as a frame with a torn sheet of paper in the top left corner. How can I solve this problem ?

I tried opening the URL to one of the pictures at home yesterday but could not open itwhereas it works from the pcs in our office. I assume the problem is one of the two mentioned by user Fabian. However i don't know how to proceed now, having close to no experience with servers etc.